The present invention relates generally to sound absorption systems and, more particularly, to both three-dimensionally-shaped, microperforated polymeric sound absorbers and methods of manufacturing the same.
Sound absorbers are in widespread use in a number of different applications. While various configurations are known, one common sound absorber design utilizes one or more layers of fibrous material to dissipate sound wave energy. Such fiber-based absorbers may include, for example, fiberglass strands, open-cell polymeric foams, fibrous spray-on materials such as polyurethanes, and acoustic tiles (agglomerated fibrous and/or particulate matter). These materials permit the frictional dissipation of sound energy within the interstitial voids of the sound absorbing material. While such fiber-based absorbers are advantageous in that they are effective over a broad acoustic spectrum, they have inherent disadvantages. For instance, these sound absorbers can release particulate matter, degrading the surrounding air quality. In addition, some fiber-based sound absorbers do not possess sufficient resistance to heat or fire. They are therefore often limited in application or, alternatively, must undergo additional and sometimes costly treatment to provide desirable heat/flame resistance.
Another type of sound absorber utilizes perforated sheets, such as relatively thick metal having perforations of large diameter. These sheets may be used alone with a reflective surface to provide narrow band sound absorption for relatively tonal sounds. Alternatively, these perforated sheets may be used as a facing overlying a fibrous sound absorber to improve sound absorption over a wider acoustic spectrum. In addition to their own absorbing properties, the perforated sheets also serve to protect the fiber-material. However, these xe2x80x9ctwo-piecexe2x80x9d sound absorbers are limited in application due to their cost and relative complexity.
Perforated, sheet-based sound absorbers have also been suggested for sound absorption. Conventional perforated, sheet-based sound absorbers may use either relatively thick (e.g., greater than 2 mm) and stiff perforated sheets of metal or glass or thinner perforated sheets which are externally supported or stiffened with reinforcing strips to eliminate vibration of the sheet when subject to incident sound waves.
Fuchs (U.S. Pat. No. 5,700,527), for example, te aches a sound absorber using relatively thick and stiff perforated sheets of 2-20 mm thick glass or synthetic glass. Fuchs suggests using thinner sheets (e.g., 0.2 mm thick) of relatively stiff synthetic glass provided that the sheets are reinforced with thickening or glued-on strips in such a manner that incident sound cannot cause the sheets to vibrate. In this case, the thin, reinforced sheet is positioned away from an underlying reflective surface.
Mnich (U.S. Pat. No. 5,653,386) teaches a method of repairing sound attenuation structures for aircraft engines. The sound attenuation structures commonly include an aluminum honeycomb core having an imperforate backing sheet adhered to one side, a perforate sheet of aluminum adhered to the other side, and a porous wire cloth adhesively bonded to the perforated aluminum sheet. According to Mnich, the sound attenuation structure may be repaired by removing a damaged portion of the wire cloth and adhesively bonding a microperforated plastic sheet to the underlying perforated aluminum sheet. In this manner, the microperforated plastic sheet is externally supported by the perforated aluminum sheet to form a composite, laminated structure which provides similar sound absorption as the original wire cloth/perforated sheet laminated structure.
While these perforated and microperforated sheet-based sound absorbers may overcome some of the inherent disadvantages of their fiber-based counterparts, they are expensive and/or of limited use. For instance, very thick and/or very stiff sound absorbers or those which require external support e.g., thickening strips, are costly and complex when compared to fiber-based sound absorbers.
Another problem inherent with fiber-based and conventional perforated sound absorbers involves applications in non-planar configurations, i.e., applications that require sound absorbers having three-dimensional rather than planar shapes. In particular, fiber-based sound absorbers generally require external support to maintain such non-planar, three-dimensional configurations. Perforated sheet-based sound absorbers, on the other hand, are heavy and typically require expensive forming equipment to produce three-dimensional shapes.
Yet another drawback with conventional, perforated sound absorbers is that the perforated sheet may require expensive, narrow diameter perforations for applications involving other than absorption of tonal sound. For instance, to achieve broad-band sound absorption, conventional perforated sheets must be provided with perforations having high aspect ratios (hole depth to hole diameter ratios). However, known punching, stamping, and laser drilling techniques used to form such small hole diameters are relatively expensive.
Accordingly, the present invention provides a shaped, broad-band sound absorber that is inexpensive to produce, yet applicable across a wide range of applications. More particularly, the present invention provides polymeric film sound absorbers having non-planar, three-dimensional shapes and methods of producing such sound absorbers.
A sound absorbing body in accordance with one embodiment of the present invention includes a polymeric film having first and second major surfaces and a plurality of microperforations extending between the first and second major surfaces. A three-dimensional shape is formed by the polymeric film. The three-dimensional shape has an interior surface and an exterior surface wherein the interior surface defines a volume.
In another embodiment, a sound absorbing body is provided including a polymeric film having first and second major surfaces and a plurality of microperforations extending between the first and second major surfaces. A three-dimensional shape formed by the polymeric film is also provided. The three-dimensional shape includes an interior surface and an exterior surface, wherein the interior surface defines a volume of the three-dimensional shape. In response to incident soundwaves at a particular frequency in the audible frequency spectrum, the sound absorbing body absorbs at least a portion of the incident soundwaves. At least a portion of the three-dimensional shape may vibrate in response to the incident soundwaves.
In yet another embodiment, a sound absorbing body is provided having a polymeric film with first and second major surfaces. The body further includes a plurality of microperforations extending between the first and second major surfaces of the polymeric film, and a three-dimensional shape formed by the polymeric film. The three-dimensional shape includes an interior surface and an exterior surface, wherein the interior surface defines a volume of the three-dimensional shape. A fibrous sound absorbing material proximate the polymeric film is also included.
In still yet another embodiment of the invention, a method of manufacturing a sound absorbing body is provided. The method includes providing a sheet of polymeric film having first and second major surfaces, wherein the polymeric film has a plurality of microperforations extending between the first and second major surfaces. The method further includes deforming the sheet to form a three-dimensional shape where the three-dimensional shape includes an interior surface and an exterior surface, the interior surface defining a volume of the three-dimensional shape.